Collagen can be prepared in sheets which extend up to 1 mm in one direction, several fm in a second, and a few unit cells thick. Such a specimen is suitable for obtaining electron diffraction data which can be treated kinematically and, therefore, analyzed to determine the crystal structure. Extending electron crystallography to macromolecules of biological interest is important for the development of this technique. Furthermore, collagen has a very long unit cell, which presents a considerable technical challenge. At present, suitable methods of preparation to yield flat unfolded sheets for examination in the EM are being developed. Preparation of the specimen is the key to successful crystallography, so when the problems presented by collagen sheets have been overcome, the solutions which were found should be applicable in a large number of other cases.